1. Field of the Invention
The present invention relates to a microphone apparatus for use in a small-size recording apparatus having an audio recording function, and more particularly to a pressure gradient type microphone apparatus having a plurality of omni-directional microphone units.
2. Description of the Prior Art
Video cameras are widely known as small-size recording apparatus having an audio recording function. Particularly, consumer-use video cameras have been remarkably reduced in size. Installation of the microphone apparatus in such small-sized consumer-use video cameras has changed from the type in which the microphone apparatus is mounted outside of the camera body to the type in which the microphone apparatus is encased in an inner space within a part of the camera body. The so-called pressure-gradient type microphone apparatus having a plurality of omni-directional microphone units has been widely used as such an encased microphone apparatus. The pressure-gradient type microphone apparatus comprises a plurality of omni-directional microphone units arranged on an outer horizontal surface of the camera body, and a directivity forming circuit for processing output signals of the plurality of microphone units. The pressure-gradient type microphone apparatus generally has the following advantages:
1) The microphone units are less affected by reflection and diffraction from the camera body, so that good sound-pickup characteristics can be obtained. PA1 2) The directivity can be changed easily.
However, the sensitivity to sound pressure of the pressure gradient type microphone apparatus is proportional to the distance between the microphone units (the distance between the centers of the sound inlets of the microphone units), i.e., the distance between acoustic terminals of the microphone units. That is, the reduction in overall size of the microphone apparatus inherently sacrifices the sensitivity to sound pressure. Accordingly, it has been difficult to largely reduce the overall size of the conventional pressure gradient type microphone apparatus while maintaining a practically required sensitivity to sound pressure.